What is the ideal tea for fermentation and aging?

The freshly plucked tea leaf has a green leafy aroma. When fresh tea leaves undergo appropriate fermentation or maturation, this green aroma becomes fruity or floral. Fermentation of tea refers to a reaction driven by the leaf's own enzymes, while maturation is a slow change that proceeds without enzymes. However, even if tea undergoes fermentation or maturation, not all teas produce fruity or floral notes.

Terpene exists both in fruits and teas

Terpenes are the main substances behind floral or fruity flavor. Terpenes are a group of compounds with isoprene as their molecular unit, and they commonly exist in fruits and flowers. The reason why the flavor of oolong or black tea is similar to fruit or flowers is because these teas contain the same substances found in them. For example, the citrus note of oolong is due to a substance called geraniol, which also exists in citrus fruits. Another common substance in tea is linalool, which also exists in lavender or bergamot. In fresh tea leaves, these terpenes are bound to sugars as terpene glycosides and have no aroma. During withering and rolling, the enzyme β-primeverosidase breaks down the glycosides, and the terpenes that give floral and fruity aromas are formed.

The more fertilizer is given, the more amino acid is formed in tea

The polyphenol content in tea is influenced by the farming method. I have studied the relationship between the amount of fertilizer and the amino acid or polyphenol content in tea. I found that the more fertilizer is applied, the less polyphenol is formed. The polyphenol content in naturally farmed tea (grown with no fertilizer) is about 3 times higher compared to ordinary tea grown with modern agricultural practices. On the other hand, tea grown with plenty of fertilizer contains a greater amount of amino acids (e.g., theanine).

Umami gives no advantage in fermentation or maturation

In terms of taste, amino acids are referred to as “umami.” In Japanese, umami has two meanings: one refers to the specific taste of amino acids, and the other means deliciousness. Due to this ambiguity, many Japanese misunderstand that more umami means better taste and higher quality. This misunderstanding is often seen in tea articles. In any case, when it comes to fermented tea, the presence of too much amino acid and less polyphenol does not lead to good flavor. Amino acids undergo the Maillard reaction when tea is fermented or oxidized without enzymes. The Maillard reaction is a reaction between amino acids and sugars or polyphenols.

Tea that is rich in polyphenol produces fruity or floral flavor

In the initial stage of the Maillard reaction, tea usually develops a flavor somewhat similar to pancakes. However, after long-term aging, the flavor can become slightly “fishy,” which is a typical smell of oxidized amino acids. This is due to further oxidation and degradation of nitrogen compounds produced by the Maillard reaction. On the other hand, tea from natural farming contains high polyphenols and low amino acids, and it develops floral or fruity flavors through long-term storage. Regarding tea aging, pu-erh tea is the most famous example. However, many other teas can also develop fruity or floral flavors if properly matured, such as Darjeeling, oolong tea and white tea. Even Japanese green tea can develop fruity flavor if well matured under certain conditions. Most importantly, the tea must be rich in polyphenols. Many famous gardens in Darjeeling practice biodynamic farming using little or no fertilizer. That is why many Darjeeling teas have intense fruity or floral flavors. This is not because polyphenols themselves create the flavor. Tea rich in polyphenols is tea that has grown slowly, and such tea also contains more terpene glycosides, the precursors of the floral and fruity flavor compounds called terpenes. On the other hand, Assam tea is generally grown with more fertilizer than Darjeeling tea, which is one reason it often gives an flavor reminiscent of pancakes.

Tea with strong aftertaste contains a lot of polyphenol

If we compare natural farming tea and tea grown with fertilizer, natural farming tea gives a stronger aftertaste. If fertilizer is applied to natural farming tea, it increases production output but drastically reduces the aftertaste. In a way, polyphenol content is proportional to the aftertaste of tea. The less nitrogen fertilizer is used, the higher the polyphenol content, and the stronger the aftertaste. With less or no fertilizer, the number of tea leaves on the tree decreases, the leaves become smaller, and the growing speed slows down. As a result, each tea leaf accumulates more minerals. If one hopes for tea to mature well, it is important to choose tea with a strong aftertaste.